1. Field of the Invention
This invention relates to a sealing device in engines for sealing the clearance between the cylinder wall and the outer surface of the piston fitted in the cylinder bore.
2. Description of Prior Art
In conventional sealing devices as shown in FIG. 3, a piston ring 5 is loosely fitted in a piston-ring groove 4 of rectangular cross section cut around the external surface of a piston 3 fitted in a cylinder bore 2 formed in a cylinder block 1, and the piston ring 5 is split at one point so that it can expand outwardly. In this case, however, since there are gaps between the piston ring 5 and the internal surfaces of the piston ring groove 4, the piston ring 5 is brought out of contact with the upper or lower surface of the piston-ring groove 4 due to inertia of the ring when the piston 3 reaches the top or bottom dead center during the reciprocating movement of the piston 3. As a result, high pressure combustion gas leaks from the combustion chamber 6, formed above the piston head 3, into the crankcase 7 as shown by the arrows (a). On the suction stroke when the pressure in the combustion chamber 6 becomes negative, lubricating oil in the crankcase 7 enters the combustion chamber 6 through the clearance between the piston ring 5 and the piston-ring groove 4. To give the piston ring 5 a tension and absorb its thermal expansion, the piston ring 5 is usually split at one point as indicated by 8 and 9 in FIG. 4. This construction has a disadvantage that the combustion gas and the lubricating oil leak through the split portions 8 and 9 and through the gap between the inner periphery of the piston ring 5 and the piston-ring groove 4 either in the direction indicated by the arrows (b) or in the opposite direction. Thus, the conventional sealing device cannot provide a sufficiently good seal between the combustion chamber 6 and the crankcase 7.